DBCC CHECKDB ballooned database

hi all:

  I have added a DBCC CHECKDB task to a database two days ago. The db itself is around 300G . Over night, it caused the database to grow 100G. First time, I thought it was an accident but this morning, I checked and the job has claimed another 100G and the database free space was also quite low.  I understand that a snapshot file will be created during the DBCC CHECKDB period but why db size was ballooned ?  I've used maintenance plan to create the dbcc checkdb task. 

I'd appreciate if anyone could give me some hints. 

thanks

hui

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